tests: move to t, allow yath test from root

By moving the tests subdirectory to t, we gain the ability to run `yath
test` with no arguments from inside `nix develop` in the root of the
the repo.

(`nix develop` is necessary in order to set the proper env vars for
`yath` to find our test libraries.)

t/jobs/darcs-update.sh

@@ -0,0 +1,24 @@
+#! /bin/sh
+set -e
+
+repo="$1"
+STATE_FILE=$(pwd)/.hg-state
+if test -e $STATE_FILE; then
+    state=$(cat $STATE_FILE)
+    test $state -gt 1 && state=0
+else
+    state=0;
+fi
+
+case $state in
+    (0) echo "::Create repo. -- continue -- updated::"
+    mkdir darcs-repo
+    darcs init --repodir darcs-repo
+    touch darcs-repo/file
+    darcs add --repodir darcs-repo file
+    darcs record --repodir darcs-repo -a -l -m "add a file" file -A foobar@bar.bar
+    ;;
+    (*) echo "::End. -- stop -- nothing::" ;;
+esac
+
+echo $(($state + 1)) > $STATE_FILE